Early age thermal conditioning immediately reduces body temperature of broiler chicks in a tropical environment

Abstract

Early age thermal conditioning (TC) durably improves resistance of broilers to heat stress and reduces body temperature (Tb). Three experiments on broiler chicks were conducted to evaluate the effects of TC at 5 d of age on Tb variation measured by thermometer between 4 and 7 d of age, under a tropical environment. Because manipulation of chickens to measure Tb with a thermometer may increase Tb, a preliminary experiment on 13 3-to-4-wk-old male broilers compared Tb measured by telemetry to Tb measured in the terminal colon during three successive periods at 22, 33, and 22 degrees C. During heat exposure, Tb rapidly increased by 0.9 degrees C and plateaued over 24 h. During the last period, seven of the broilers rapidly reduced Tb to a plateau lower than the initial Tb, although six broilers exhibited more variable Tb. Measurement by thermometer underestimated on average core Tb by 0.28 degrees C at 22 degrees C and by 0.57 degrees C at 33 degrees C, whereas Tb recorded by telemetry was not affected by manipulation of the chickens. TC reduced Tb 24 h later in the three experiments. Compared to unexposed control chicks (N), 12 h of TC at 40 degrees C did not significantly reduce Tb at 7 d of age, although 24 h did. TC at 38 and 40 degrees C over 24 h significantly reduced Tb variation from 4 to 7 d of age compared to N chicks, whereas 36 degrees C did not. Withdrawing feed from the chicks for 2 h prior to measurement did not significantly reduce Tb at 4 and 7 d of age, but Tb reduction due to TC was greater in fed chicks (0.28 degrees C) than in chicks without feed (0.05 degrees C). Early age thermal conditioning at 38 to 40 degrees C at 5 d of age for 24 h reduced body temperature of 7-d-old male broilers.

Does early thermal conditioning sometimes fail to improve the resistance of broilers to heat stress?

“…In the three experiments, Tb at 7 days of age was reduced by TC as described earlier [11,12] and this reduction remained consistent until the end of the production period, in agreement with earlier findings [3,26,28]. Recent results showed that TC induces the stimulation of gut development and activity, reduces the circulating level of T3 and increases feed intake during the 48 hours following TC [25].…”

“…Optimal penetration according to the size of the chickens and timing were determined by preliminary trials. Simultaneous telemetry recordings confirmed that Tb was not affected by the manipulation of the chickens [12]. Tb was measured in all chicks at 4 and 7 days of age, i.e.…”

Cyclic variations in incubation conditions induce adaptive responses to later heat exposure in chickens: a review

“…Furthermore, the body temperature of chicks exposed to 38°C at 5 day posthatch remained significantly lower than that of controls up to 40 days in tropical conditions . Body temperature was shown to be an accurate indicator of thermotolerance of endotherms under a wide range of ambient temperatures, including chickens during their life span (De Basilio et al, 2003): chickens that died during heat challenge at 34 day had higher body temperatures (+0.6°C)…”

“…Although postnatal TM seems to be an interesting technique, there are limitations to applying it on a large scale because of the difficulties of maintaining 38°C homogeneously for 24 h in the poultry house. It depends on the type and efficacy of the heat source (De Basilio et al, 2003) and on the poultry house insulation. TM during embryogenesis, performed directly in incubators, may therefore be easier for the poultry industry to apply.…”

Effect of Short-Term Thermal Conditioning on Physiological and Behavioral Responses to Subsequent Acute Heat Exposure in Chicks

“…The age for the thermal conditioning applied in this study was referred to the previous reports (De Basilio et al, 2001Basilio et al, , 2003. Thereafter, treatment chicks were exposed to high temperature at 40℃ for 3 h while control chicks were kept at 30℃.…”